Aluminium alkoxides: A family of versatile initiators for the ring‐opening polymerization of lactones and lactides

Abstract

Aluminium alkoxides, such as Al(OiPr)3 or Et3‐pAl(O (CH2)2X)p with 1≤p≤3, are very effective in initiating the polymerization of lactones, e.g.ϵ ‐ca‐prolactone and δ ‐valerolactone, and lactides (D,L‐ or L,L‐ isomers). The ring‐opening polymerization proceeds through a “coordination‐insertion” mechanism that involves the selective rupture of the acyl‐oxygen bond of the monomer and its insertion into an Al‐O bond of the initiator. Polymerization is typically “living” and allows block copolyesters with perfectly controlled molecular weight and composition to be prepared. Aluminium alkoxides carrying functional alkoxy groups (X = ‐Br, ‐CH2‐NEt2, ‐CH2‐CH=CH2, ‐CH2‐OC(O)‐C(Me)=CH2…) provide asymmetric telechelic polyesters (end‐groups being ‐X and ‐OH, respectively) and very interesting polyester macromonomers. Coupling the asymmetric telechelic chains via the hydroxyl end‐group ‐ or better its A1 alkoxide precursor ‐ is a straightforward way to the symmetric telechelic polymer bearing the X functional group.

?-Caprolactone/ZnCl2 complex formation: Characterization and ring-opening polymerization mechanism

“…[1][2][3][4][5] In this way, some organometallic compounds such as alkylmetals have been also used in polyester synthesis.…”

Poly(?-caprolactone-b-glycolide) and poly(D,L-lactide-b-glycolide) diblock copolyesters: Controlled synthesis, characterization, and colloidal dispersions

“…Because the experimental details have been published elsewhere, 18,19,25 only key points are emphasized here.…”

“…The universal calibration method was made possible by the availability of the viscometric relationships valid for PD,L-LA and PCL in THF at 30°C: 18,19,25 ͓͔ ϭ 1. 25 Low molecular weights were also calculated from 1 H NMR spectra on the basis of the relative intensity of the protons in the ␣ position of the hydroxyl end group and the intramolecular ester groups, respectively.…”

“…4 -11 Compared with PLA and PGA, PCL degrades more slowly. 12 It has been reported elsewhere that aluminum alkoxides are effective initiators for the controlled ring-opening polymerizations of lactones, lactides, [13][14][15][16][17][18][19] dioxepan-2-one, 20 and cyclic anhydrides 21 with the formation of (co)polyesters and polyanhydrides of predictable molecular weights and low polydispersities. A living coordinationinsertion mechanism has been reported that is based on the insertion of the monomer into the AlOO bond of the initiator through the selective acyl-oxygen cleavage of the ring.…”

“…As a direct extension of this mechanism, functional aluminum alkoxides, such as (C 2 H 5 ) 3Ϫp AlO(ORX) p where X is a functional group (halogen, tertiary amine, unsaturation …), have been successfully used in the synthesis of end-reactive PCL 18 and PLA 19 chains.…”